In the drive train of a motor vehicle, various components are arranged such as the vehicle engine, engine ancillary equipment (for example, current generator, climate control system), a clutch, a torque converter, a transmission having a transmission ratio which can be varied, a differential transmission and/or the driven vehicle wheels. To optimize the drive train control, it is necessary to use information as to the actual load state or the actual traction resistance of the vehicle. An increased traction resistance occurs, for example, when driving uphill and by a change of the drag coefficient of the vehicle. An increased traction resistance generates a driving situation to which the control of the drive train should react in a suitable manner. Especially, an adaptation of the strategy for transmission ratio determination is advantageous.
Electronic transmission controls are provided with algorithms for detecting load or traction resistance. Shift characteristic lines are shifted and/or further measures are initiated to avoid up and down gear shifting in dependence upon the detected load or the detected traction resistance. For the detection, a comparison of the actual vehicle longitudinal acceleration to the expected vehicle longitudinal acceleration is made, for example. For this purpose, the expected vehicle longitudinal acceleration is to be determined.
The Patent DE 30 18 032 C2 (U.S. Pat. No. 4,625,590) describes a method wherein the expected vehicle longitudinal acceleration is determined with the aid of the output torque. Here, the efficiency of the drive train is considered. The result determined in this manner is, however, only correct for steady-state driving operation because the torques, which are required for acceleration and deceleration of the rotating masses in the drive train, are not considered.
A method is described in DE 41 38 822 C2 (U.S. Pat. No. 5,557,519) wherein the mass of the vehicle is increased by a "rotation mass" in order to compensate for this effect. This procedure however requires a gear-dependent correction of this "rotation mass".